For welding a tack-welded cylindrical vessel such as a pressure vessel along an outer surface groove and an inner surface groove formed thereon, it is the conventional practice to use manual welding or to assemble a self-travelling welding machine in the cylindrical vessel for welding.
However, a manual welding has a low efficiency, and when welding a cylindrical vessel along an inner surface groove formed thereon, inconvenience is inevitable that welding cannot be accomplished unless the operator enters the narrow space within the cylindrical vessel. On the other hand, since a self-travelling welding machine gives an unstable travel, it is impossible to conduct high-speed welding.
Under such circumstances, there is a demand for development of an apparatus for automatically welding a tack-welded cylindrical vessel at a high efficiency along an outer surface groove and an inner surface groove formed thereon, but such a welding apparatus has not as yet been proposed.